1. Field of the Invention
The invention relates to an image sensor structure and method of fabricating the same, and more particularly to a photodiode layer of a photoconductor on active pixel (POAP) image sensor structure and method of fabricating the same.
2. Description of the Related Art
Photoconductor on active pixel (POAP) image sensors are widely applied in many fields such as digital cameras, digital video cameras, monitors and mobile phones. POAP image sensors employ photoconductors, such as photoconductor covered active pixels or image sensor cell arrays, to convert optical light into electrical signal.
POAP image sensors are capable of detecting light of various wavelength such as visible light, X-ray, ultraviolet (UV) and infrared ray (IR). Electrons are generated by incidental light absorbed by photoconductors formed on the top of POAP image sensors, and transported to circuits below the photoconductors. Compared with conventional image sensors, POAP image sensors have higher photosensitivity, better light collection, and higher pixel density. FIG. 1 is a cross sectional view of a conventional POAP image sensor structure 10. An incident light passes through a transparent conductive layer 145 in a pixel area (N-1, 1) or (N, 1) to a photodiode structure 135. The photodiode structure 135 converts the incident light into an electrical signal and transports the electrical signal to an active region 130 in a substrate 11.
A dark environment is desirable for POAP image sensors to achieve advantages such as high image quality, low crosstalk, low noise and high quality image. In the conventional POAP image sensor structure 10, however, the photodiode structure 135 in different pixel areas (N-1, 1) and (N, 1) is a continuous layer as shown in FIG. 1. Incident light with a large angle radiates in a pixel area (N-1, 1). The electrical signal converted by the photodiode structure 135 in the pixel area (N-1, 1) is transported to the active region 130 of the adjacent pixel area (N, 1) due to the continuous photodiode structure 135. Crosstalk may occur when current flows from higher-potential pixel area (N-1, 1) to neighboring, lower-potential, pixel area (N, 1). Crosstalk results in blurred image, reduces resolution, and color transposition. Thus the performance of the image sensor structure suffers. The crosstalk problem is more serious when the density of the image sensor is increased by shrinking the pixel area or using a multi-layer dielectric structure.
An image sensor structure with low crosstalk capable of solving the described problems is desirable.